Site specific control of the crystallographic orientation of grains within metal components has been unachievable before the advent of metals additive manufacturing (AM) technologies. To demonstrate the capability, the growth of highly misoriented micron scale grains outlining the letters D, O and E, through the thickness of a 25·4 mm tall bulk block comprised of primarily columnar [001] oriented grains made of the nickel base superalloy Inconel 718 was promoted. To accomplish this, electron beam scan strategies were developed based on principles of columnar to equiaxed transitions during solidification. Through changes in scan strategy, the electron beam heat source can rapidly change between point and line heat source modes to promote steady state and/or transient thermal gradients and liquid/solid interface velocity. With this approach, an equiaxed solidification in the regions bounding the letters D, O and E was achieved. The through thickness existence of the equiaxed grain structure outlining the letters within a highly columnar [001] oriented bulk was confirmed through characterizing the bulk specimen with energy selective neutron radiography and confirming with an electron backscatter detection. Ultimately, this demonstration promotes the ability to build metal components with site specific control on crystallographic orientation of grains using the electron beam melting process.
Two optical configurations are commonly used in single-molecule fluorescence microscopy: point-like excitation and detection to study freely diffusing molecules, and wide field illumination and detection to study surface immobilized or slowly diffusing molecules. Both approaches have common features, but also differ in significant aspects. In particular, they use different detectors, which share some requirements but also have major technical differences. Currently, two types of detectors best fulfil the needs of each approach: single-photon-counting avalanche diodes (SPADs) for point-like detection, and electron-multiplying charge-coupled devices (EMCCDs) for wide field detection. However, there is room for improvements in both cases. The first configuration suffers from low throughput owing to the analysis of data from a single location. The second, on the other hand, is limited to relatively low frame rates and loses the benefit of single-photon-counting approaches. During the past few years, new developments in point-like and wide field detectors have started addressing some of these issues. Here, we describe our recent progresses towards increasing the throughput of single-molecule fluorescence spectroscopy in solution using parallel arrays of SPADs. We also discuss our development of large area photon-counting cameras achieving subnanosecond resolution for fluorescence lifetime imaging applications at the single-molecule level
2The spontaneous imbibition of water and other liquids into gas-filled 3 fractures in variably-saturated porous media is important in a variety of 4 engineering and geological contexts. However, surprisingly few studies have 5 investigated this phenomenon. We present a theoretical framework for 6 predicting the 1-dimensional movement of water into air-filled fractures 7 within a porous medium based on early-time capillary dynamics and 8 spreading over the rough surfaces of fracture faces. The theory permits 9 estimation of sorptivity values for the matrix and fracture zone, as well as a 10 dispersion parameter which quantifies the extent of spreading of the wetting 11 front. Quantitative data on spontaneous imbibition of water in unsaturated 12 Berea sandstone cores were acquired to evaluate the proposed model. The 13 cores with different permeability classes ranging from 50 to 500 mD and 14 were fractured using the Brazilian method. Spontaneous imbibition in the 15 fractured cores was measured by dynamic neutron radiography at the 16 Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge 17 National Laboratory. Water uptake into both the matrix and the fracture 18 zone exhibited square-root-of-time behavior. The matrix sorptivities ranged 19 from 2.9 to 4.6 mm s -0.5 , and increased linearly as the permeability class 20 increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 21 mm s -0.5 , and increased linearly with increasing fracture aperture width. The 22 dispersion coefficients ranged from 23.7 to 66.7 mm 2 s -1 and increased 23 linearly with increasing fracture aperture width and damage zone width. 24 Both theory and observations indicate that fractures can significantly 25 increase spontaneous imbibition in unsaturated sedimentary rock by 26 capillary action and surface spreading on rough fracture faces. Fractures 27 also inrease the dispersion of the wetting front. Further research is needed 28 7
Conventional neutron radiography can be strongly enhanced by obtaining Bragg‐edge information spatially correlated with the attenuation coefficient. This can now be achieved through time‐of‐flight techniques at pulsed neutron sources, utilising a neutron counting detector with high‐spatial and high‐temporal resolution. In these measurements, the positions of Bragg edges can in principle be obtained for each 55 × 55 μm2 pixel of the radiographic image. The combination of both Bragg‐edge and attenuation information enables high spatial resolution studies to be carried out on material composition, phase transitions, texture variations, as well as residual strain mapping. In this article, we present the results of high‐resolution strain maps of a ferritic steel cantilever sample measured at different loads by both transmission and conventional diffraction modes, as well as strains in an austenitic steel compact‐tension (CT) crack sample. The proof of principle experiments performed on the ENGIN‐X beamline on a bent cantilever arrangement resulting in a uni‐axial stress field verified that the strain values measured in diffraction and transmission mode are in good agreement. The characteristics of the transmission mode detector as well as the measured strain maps and future possibilities of this technology are discussed.
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